 class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}

class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode curN = null;
        ListNode cur = head.next;
        ListNode prev = head;
        prev.next = null;

        while (cur != null) {
            curN = cur.next;
            cur.next = prev;
            prev = cur;
            cur = curN;
        }

        return prev;
    }
}